This invention relates to high voltage, high power circuit interrupters and more specifically relates to an interrupter of the puffer type and which uses a relatively low volume of liquid SF.sub.6 l as an interruption medium.
High voltage, high power circuit interrupters using SF.sub.6 gas blast principles for arc interruption are well known and are in general use in electrical utilities. one popular form of an SF.sub.6 gas blast interrupter uses a two-pressure system design in which high-pressure SF.sub.6 is released to flow through the separating contacts of the interrupter and into a relatively low-pressure region during interruption. This type device requires auxiliary equipment for compressing the gas and monitoring the operating pressures. The operating pressures of the two-pressure system are also limited by the dew point of the gas and, in most cases, external heaters are needed to prevent liquefaction of the SF.sub.6 gas. These constraints on operating pressure limit the performance of the interrupter since interrupting performance is improved and higher interrupting ratings can be achieved by increasing the pressure both upstream of the contacts and downstream of the contacts.
To eliminate the need for a dual-pressure system, and in many instances the need for external heaters, it is possible to use an SF.sub.6 puffer type breaker in which SF.sub.6 gas is moved through the separating interrupter contacts by a piston type device which moves with the movable interrupter contact element. In a puffer type device, however, only moderate pressure differentials can be obtained if the operating mechanism is to be of a practical design, so that the interrupting capability of the gas type SF.sub.6 puffer interrupter is limited. In addition, the interrupting time of a puffer type interrupter is relatively long because relatively long strokes are needed to effect the necessary gas compression. One puffer device which is of this type, but which uses a compression and a decompression gas chamber on opposite sides of the nozzle, is shown in U.S. Pat. No. 3,987,261, in the name of McConnell, dated Oct. 19, 1976.
The use of liquid sulfur hexafluoride for circuit interruption purposes has been contemplated in the past. However, problems of cavitation and the like have limited the usefulness of these devices. One patent disclosing the use of liquefied sulfur hexafluoride for a circuit interrupter is U.S. Pat. No. 4,009,358. This patent teaches the use primarily of a single piston in which the SF.sub.6 liquid on one side of the piston communicates with the other side of the piston over a relatively long path.